The invention relates to a control specimen for evaluation of non-destructive test results and for the comparison of results measured on metal work piece vs. results measured on the control specimen, furthermore for the production of artificial inclusions used in control specimens, and a process for producing said control specimens.
The propagation and development of the ultrasonic method are most dynamic among the non-destructive test methods used for checking the internal structural imperfections of joints and parts made of metal. Apart from the numerous economic and technical benefits of its applicability, it is indisputable that interpretation of the ultrasonic signals received during testings and the evaluation referring to the character and magnitude of the defects detected in the joint generally lag behind the qualitative requirement level demanded by the designers.
In the course of checking by radiographic method, the defects of the material appear in projection, where determination of the extension of the imperfections represents uncertainty. In order to reduce the shortcomings of the evaluation in the non-destructive methods and to reproduce the test results, various methods have been developed and each can be traced back to the application of of certain standard type.
The control specimens presently used for ultrasonic testing of joints are divided into three groups:
internationally recognized, standardized control specimens, made of highly reliable, unalloyed steel, the geometry of which is independent from the purpose of the test, PA1 individual, welded control specimens, the formation of which is somehow connected with the test piece (material, surface, geometry, etc). PA1 individual control specimens without welding, the thickness, material and surface quality of which are similar to those of the test piece.
Use of the three standard type can be traced back to the same principle, i.e. that the signals received on the oscilloscope with the aid of reference surfaces formed on the control specimen (rear wall, bottom hole perpendicular to the ultrasonic beam of rays, hole perpendicular to and parallel with the tested surface) can be compared with the signals received during the tests on basis of the amplitudes. The comparison serves for determination of the testing technology (gemetric and sensitivity calibrations) and for reproduction of the results. The indices obtained from the use of standard types refer only to the signal magnitudes received from the reference surfaces, and do not give any direct connection for determination of the actual extent and character of the faults. Identical signal levels--depending on the location, fault type, orientation--may represent 200-300% dimensional difference. Accordingly, conversion of the ultrasonic test results is presently unsolved for the designer's requirements in respect of the actual size of the imperfect joint.
Ultrasonic holography is a very expensive laboratory procedure, which increases the accuracy of fault estimation with the aid of an oscillator having an electronically variable sound space.